1. Field of the Invention
The present invention relates to the field of power generation systems. More particularly, the present invention is directed to a novel oxygen-fired power generation system offering a combination of temperature controls and power generation mechanisms to achieve a higher power generation efficiency than that provided by the prior art. Specifically, an oxygen fired power generation system is provided having a high pressure combustor having a water recycle temperature control subassembly, and an intermediate pressure combustor having a CO2 recycle temperature control subassembly. Thus, a first energy cycle utilizes a first energy source operatively associated with a corresponding first heat sink, and a first inert agent to provide energy transfer therebetween and temperature control during operation of the first energy source. In like fashion, a second energy cycle utilizes a second energy source operatively associated with a corresponding second heat sink, and a second inert agent to provide energy transfer therebetween and temperature control during operation of the second energy source. The first and second energy sources are not identical, the first and second heat sinks are not identical and the first and second inert agents are not identical.
The first and second energy cycles are configured in combination to provide a power generation unit.
2. Description of the Prior Art
Oxygen-fired, zero-emission power generation schemes have been proposed in the past. For example, the schemes proposed by Beichel, et al. (U.S. Pat. Nos. 5,715,673 and 5,956,937) are based on a process in which a high-pressure combustor is fired with oxygen, gaseous fuel, and water to produce a drive gas for a steam turbine. The discharge from this turbine may be reheated in an intermediate pressure combustor fired with additional fuel and oxygen. The discharge from this combustor then enters a gas turbine to generate additional power. The discharge enters a condenser to separate water, and the carbon dioxide-rich effluent is either vented or compressed, treated, and sold or delivered to a sequestration site.
A method for operating a boiler using oxygen-enriched oxidants is disclosed in U.S. Pat. No. 6,314,896, issued to Marin on 13 Nov. 2001. This invention generally discloses a method for operating a boiler in which oxygen-enriched air is introduced with a fuel into the combustion space within a steam-generating boiler.
Another scheme that has been proposed for the generation of power using steam and gas turbines was proposed by O. Bolland and S. Saether in ENERGY CONVERSION & MANAGEMENT, Vol. 33, Nov. 5–8, 1992, p. 467. The Bolland/Saether scheme consists of supplying a combustor with oxygen from an air separating unit (“ASU”), reacting the oxygen with a fuel, adding water or steam to control the combustor outlet temperature, and passing the combustor gases through a turbine to generate power. In this heat recovery system, a water inlet stream is used to cool the discharge of the ASU main compressor.
Another scheme that has been proposed, by E. I. Yantovskii in PROCEEDINGS OF WORLD CLEAN ENERGY CONFERENCE, Geneva, Switzerland, 1991, pp. 571–595, discloses using oxygen-fired combustion in conjunction with a water recycle. A high-pressure combustor receives oxygen from an ASU, hydrocarbon fuel, and recycled water and produces a steam/CO2 drive gas that enters a turbine. This is followed by two stages of reheating and expansion. The CO2 is separated in a condenser, and the condensate is recycled to the high-pressure combustor. The cycles described are purportedly capable of attaining relatively higher efficiencies, but this is contingent upon the development of advanced steam turbines.
In a process known as the “Matiant” cycle, PROCEEDINGS OF THIRD INTERNATIONAL CONFERENCE ON CARBON DIOXIDE REMOVAL (ICCDR-3), Boston, 1996, a drive gas for a gas turbine is produced by combusting with oxygen and recycled CO2. The drive gas enters a turbine operating at pressures and temperatures characteristic of gas turbines. The turbine discharge enters a heat recovery device such as a heat recovery steam generator, is cooled, and water is separated. A portion of the CO2-rich effluent is recycled to the combustor and the remainder is vented or compressed. Variations of this concept also incorporate techniques to liquify, heat, and expand the CO2 product, as disclosed, for example, in U.S. Pat. No. 5,802,840. Similar schemes are described in U.S. Pat. Nos. 3,736,745, 4,434,613, 4,498,289, 5,175,995, 5,247,791 and 5,265,410.
Although these cycles purport to enable higher efficiency energy production, they are dependent on the development of increasingly high pressure, high temperature turbines which are not currently available.
In contrast to the Matiant cycle, the “Graz Cycle” is described in the literature at ASME paper 95-CTP-79, ASME COGEN-TURBO POWER CONFERENCE, Vienna, Austria (1995), and also in CIMAC paper G07, CIMAC CONFERENCE, Interlaken, Switzerland (1995). In this cycle, a high-pressure combustor is fired with fuel, oxygen, steam, and recycled CO2/steam. The stream leaving the combustor is expanded in a high-pressure turbine and enters a heat recovery system to generate pure steam, which subsequently enters a steam turbine. The discharge from the steam turbine then enters the combustor. After the heat recovery unit, a portion of the high pressure turbine discharge is compressed and recycled back to the combustor. The remaining portion enters a low pressure turbine and a water removal system.
In contrast to the foregoing proposals and power generation systems, the present invention provides an oxygen fired power generation system having a high pressure combustor having a water recycle temperature control subassembly and an intermediate pressure combustor having a CO2 recycle temperature control subassembly.
A problem associated with power generation systems that precede the present invention is that utilize a single inert agent as a temperature control agent, thereby limiting the cycle flexibility.
Another problem associated with power generation systems that precede the present invention is that they utilize a gaseous inert agent, such as CO2, at high pressure, thereby necessitating compression of the gaseous inert agent to facilitate its fluid flow from the separator to the combustor.
Still another problem associated with power generation systems that precede the present invention is that they utilize a multi-phase inert agent, such as water, at high temperature, thereby necessitating condensation of the multi-phase inert agent and the concomitant heat loss thereby to facilitate its fluid flow from the separator to the combustor.
In contrast to the foregoing, the present invention provides a power generation system that seeks to overcome the foregoing problems and provide an optimized power generation system that reduces the fuel consumption, and the required investment, due to the variety of parts compressors, condensers, etc.) that can be adapted for use with the power generation cycle disclosed herein.